Manufacture of carbon-bonded alumina based on a lactose-tannin binder system via slip casting

Binders play an important role in the manufacture of carbon-bonded alumina (Al₂O₃-C) refractory materials. To diminish the currently used coal tar pitch binder Carbores® P, which could release hazardous polycyclic aromatic hydrocarbons during operations, environmental-friendly lactose and tannin are applied as the main binders in this study. Compact cylinders of fine-grained Al₂O₃-C based on the lactose-tannin (16 wt%) binder system with significantly reduced pitch content (4 wt%) are successfully prepared via slip casting for the first time. The lactose to tannin mass ratio is systematically varied from 5:1 to 1:5 in the raw material formulation. The specimens based on the new binder system are less dense, more porous and contain less residual carbon than the pitch-based reference. Mechanical tests show that the specimens with lactose-tannin ratio of 5:1, 4:1 and 3:1 have considerable cold crushing strengths, although the splitting tensile strengths are low. In contrast to the well-established pressing route, the slip casting route for compact Al₂O₃-C is more comparable to the replica route for Al₂O₃-C foam filter due to the pressureless shaping process.